1. Field of Invention
This invention relates generally to portable electronic devices and more particularly to devices with improved usability.
2. Discussion of Related Art
Many portable electronic devices contain audio interfaces, such as speakers and/or microphones, that allow users to exchange information with the portable device in audio form. Audio interfaces often have controls that allow users to adjust the volume of sound produced by the audio interface so that the users can use the devices in multiple modes. For example, many mobile devices give users the option of holding the mobile device close to their ears or to adjust the volume of sound produced by the device so that users can hear sound when the device is held away from their ears.
Present mobile devices generally rely on manual control to adjust the gain of the speaker so that the sound volume is set based on the desired mode of use. A drawback of such an approach is that users may place the device near their ears when the volume is turned up. As a result, the user might experience sound pressure levels that are unpleasant and possibly damaging to their ears.
Some devices employ methods that help prevent users from being exposed to high sound pressure levels if the users forget to reduce the volume level before placing the device near their ears. One such method, incorporated into some cellular telephones, utilizes a fade-in method. The speaker driver in the phone modifies the sound to be played by the device to fade-in any sound coming out of the device. The gradual fade-in prevents any sudden blasts of sound and gives users a chance to move their phones from their ears before sound levels reach an uncomfortable level.
Another approach used in current devices is to provide a dual speaker system. Mobile devices with dual speaker systems contain one speaker in a surface of the device intended to be placed near a user's ear and another speaker on the opposite side. The speaker intended to face the user emits low sound pressure levels and is intended for use when the device is held close to the user's face. The speaker facing away from the user can emit larger sound pressure levels and is intended for use when the device is held away from the user's face.
A similar issue arises for portable devices that include microphones designed to pickup a user's voice. Problems in picking up the voice signal can also occur when users may move the device close to their mouths or away from their mouths. Automatic Gain Control (AGC) is one method for dealing with the differences in sound pressure levels at the microphone caused by users changing the distance between devices and their mouths. AGC sets the gain of the microphone based on the power level of the signal picked up by the microphone. When a signal is strong, such as when users talk with the devices held close to their mouths, the gain is reduced. When a signal is weak, such as when users talk with the devices held away from their mouths, the gain is increased.